Identification Of The Sugar Transporter Gene Families And Study On The Functions Of Two Hexose Sugar Transpoters In Malus Domestica

Sweetness is one of the most important factors in the fruit quantity, and depends on the concentration of sugars in fruit, transportation and storage of which needs the sugar transporters. Clear about the information of the sugar transporters in Malus dometica and study the functions of key sugar transporters in apple fruit are necessary to improve the fruit quality. This research identified the sugar transporter gene families, analyzed their functions in sugar accumulation expression,cloned two hexose sugar transporters, conducted the subcellular localization,transformed the two genes into apple fruit and Solanum lycopersicum to find out their functions.The main results are as follows:Identified 31 sugar alcohols [including 17 sorbitol transporters(SOTs)], 9 sucrose transporters, 50 monosaccharide transporters and 27 SWEET genes by cluster analysis. Then compared their homology and cleared their evolution relationship and named them according to the phylogenetic tree.Conducting the expression profiling of these genes which are related to the accumulation of fruit sugars in different tissues and developed fruit of ‘Gala’ apple,and we found that 68 of them transcribed and owning different expression models. With analyzing the relationship between their expression and sugar accumulation, the results showed that the high accumulation of fructose in apple fruit was possibly linked to the coordination between MdTMT1/2 and MdEDR6.MdEDR6.7 and MdHT2.2, which have significant correlation with sugar accumulation, were cloned, MdEDR6.7 comprising a 1464 bp ORF(open reading frame) encoding 488 amino acids and MdHT2.2 having a 1569 bp ORF encoding 523 amino acids. Both of them have 99% homology with the relevant sequence in Malus domestica genome. Subcellular localization showed that MdEDR6.7 was on the tonoplast while MdHT2.2 located on the plasma membrane.With transforming MdEDR6.7 into apple fruit callus ‘wang lin’, the transgenic lines had a lower Glc content,yet the content of Fru changed little. They thrived on the 3% glucose medium and had a great increasing in whole mass and dry matter because of MdEDR6.7 involving in Glc efflux from the vacuole.Transforming MdEDR6.7 and MdHT2.2 into Solanum lycopersicum, we noticed that MdEDR6.7 transgenic lines had bigger leaf area and stem diameter, but a lower in hight and a decreased Glc content. Transgenic Solanum lycopersicum of MdEDR6.7 also showed a lower in hight, decrease of Glc and Fru, but the Suc changed not much.